Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, and various signal processing circuits.
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual images for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
FIG. 1 illustrates electronic device 50 having a chip carrier substrate or printed circuit board (PCB) 52 with a plurality of semiconductor packages mounted on a surface of the PCB. Electronic device 50 can have one type of semiconductor package, or multiple types of semiconductor packages, depending on the application. Different types of semiconductor packages are shown in FIG. 1 for purposes of illustration.
Electronic device 50 can be a stand-alone system that uses the semiconductor packages to perform one or more electrical functions. Alternatively, electronic device 50 can be a subcomponent of a larger system. For example, electronic device 50 can be part of a tablet, cellular phone, digital camera, or other electronic device. Electronic device 50 can also be a graphics card, network interface card, or other expansion card that is inserted into a personal computer. The semiconductor packages can include microprocessors, memories, application specific integrated circuits (ASIC), programmable logic circuits, analog circuits, radio frequency (RF) circuits, discrete devices, or other semiconductor die or electrical components.
In FIG. 1, PCB 52 provides a general substrate for structural support and electrical interconnect of the semiconductor packages mounted on the PCB. Conductive signal traces 54 are formed over a surface or within layers of PCB 52 using evaporation, electrolytic plating, electroless plating, screen printing, or other suitable metal deposition process. Signal traces 54 provide for electrical communication between each of the semiconductor packages, mounted components, and other external system components. Traces 54 also provide power and ground connections to each of the semiconductor packages. A clock signal is transmitted between semiconductor packages via traces 54.
In some embodiments, a semiconductor device has two packaging levels. First level packaging is a technique for mechanically and electrically attaching the semiconductor die to an intermediate substrate. Second level packaging involves mechanically and electrically attaching the intermediate substrate to the PCB. In other embodiments, a semiconductor device may only have the first level packaging where the die is mechanically and electrically mounted directly to the PCB.
For the purpose of illustration, several types of first level packaging, including bond wire package 56 and flipchip 58, are shown on PCB 52. Additionally, several types of second level packaging, including ball grid array (BGA) 60, bump chip carrier (BCC) 62, land grid array (LGA) 66, multi-chip module (MCM) 68, quad flat non-leaded package (QFN) 70, quad flat package 72, embedded wafer level ball grid array (eWLB) 74, and wafer level chip scale package (WLCSP) 76 are shown mounted on PCB 52. Depending upon the system requirements, any combination of semiconductor packages, configured with any combination of first and second level packaging styles, as well as other electronic components, can be connected to PCB 52. In some embodiments, electronic device 50 includes a single attached semiconductor package, while other embodiments call for multiple interconnected packages. By combining one or more semiconductor packages over a single substrate, manufacturers can incorporate pre-made components into electronic devices and systems. Because the semiconductor packages include sophisticated functionality, electronic devices can be manufactured using less expensive components and a streamlined manufacturing process. The resulting devices are less likely to fail and less expensive to manufacture resulting in a lower cost for consumers.
A manufacturer of electronic device 50 provides a clock signal to each semiconductor package to operate the synchronous logic elements within each package. Digital circuits of the semiconductor packages include flip-flops or latches which operate on edges of the clock signal. A binary digital value is either a logic zero or a logic one. A clock signal rapidly fluctuates between a logic zero and logic one. When a clock signal transitions from a logic zero to a logic one, the transition is a rising edge of the clock signal. When a clock signal transitions from a logic one to a logic zero, the transition is a falling edge of the clock signal. A logic one is commonly a VDD voltage or other voltage node used to power the electronic device. A logic zero is commonly a ground voltage node or zero volts.
In many embodiments of electronic device 50, the electronic device is able to enter a low-power sleep state. While electronic device 50 is in a low-power state, the clock signal is still used for certain functions, including to allow the electronic device to wake up from the sleep state. Therefore, electronic component manufactures desire to reduce the power consumption of clock generation circuitry. Reducing the power consumption of a clock that runs while an electronic device is sleeping increases the amount of time that a battery powering the device lasts between battery charges.
In addition, many electronic devices 50 are used in situations where the ambient temperature can vary widely. Manufacturers of electronic products desire clock signal generation circuitry that does not vary significantly as a function of temperature.